The present invention relates to a device for indicating ice formation on, for example, a road surface, the wing of an airplane, or an electric power line using a sensor sensitive to heat released during the ice formation.
A device for indicating ice formation can for example have the properties, disclosed in the Swiss Patent publication 506 850 for indicating a commencing of ice formation on a road surface. Here, a sensor with a Peltier element encompassed in a cap is embedded in the road surface coating at a short distance spaced below the surface. Further, at a distance apart from each other, two temperature sensors are embedded in the road surface coating and are by means of two electric wires connected to a connecting device inside the cap. The Peltier element""s lower contact surface is connected to a metal plate, which plate constitutes a heat dissipating reference surface to the road surface, and its upper contact surface is connected to one of the temperature sensors by a thick conductor made of copper. The contact surfaces are connected to a current source with such a polarity that the upper contact surface is cooled, so that the copper conductor and the adjacent temperature sensor are in turned cooled. This means that when the outside temperature is decreasing and the road surface is cooled towards 0xc2x0 C., this will primarily result in a freezing into ice of moisture or water onto the temperature sensor, which is cooled by the Peltier element. The formation of ice is remotely recorded as a temperature rise by the cooled temperature sensor by means of an apparatus for signal processing which is suitably placed and connected to the two temperature sensors. If the outside temperature decreases further, moisture and water on the road surface will freeze as well as on the second temperature sensor. This second sensor will also indicate a temperature rise in the apparatus for signal processing as a sign that ice formation on the road surface has occured. The distance between the temperature rises represents the time of fore-warning by means of which the indication of a present risk for ice formation is alarmed.
The device is however afflicted with several deficiencies. First, if a continuous decrease of temperature does not occur after the artificially cooled temperature sensor has indicated ice formation, a false warning occurs. Second, the device demands quite a lot of space and thus it is difficult to integrate into, for example a metal sheet. The third and most serious deficiency is however the fact that ice formation often occurs without any temperature increase in the surface of interest. For example, this is the case of slow cooling down of a wet surface. In connection with the formation of ice, an equalization of the temperature only takes place at 0xc2x0 C., and thereafter the temperature decreases after all the water has frozen. Thus, in this case there will be no indication of occured ice formation.
The purpose of the invention is to produce a simplified device, that will secure the indication of ice formation almost in the very moment it occurs, and which also can be used to control how long the formed ice remains. Further, it is a purpose of the invention to provide a device which is easy to integrate with different objects where ice may form.
By endowing the device for indication of ice formation with the characteristics stated in the accompanying claims, the above stated purposes have been obtained through this invention. As the changes of temperature of the measuring surface is an unreliable indicator of the occurance of ice formation, according to what is stated above, the heat flow that always is released when ice forms will be used instead. The major quantity of heat released in connection with the formation of ice will penetrate the measuring object, and will thereby affect the heat flow that passes through the object. A commonly used method for recording heat flow is to measure the temperature difference between two closely spaced points in the direction of the heat flow. Especially useful is a Peltier element which is used in this invention.
The device according to the invention is extremely compact and easy to integrate with different surfaces. The sensor in itself may be designed as an easily integrated, small canister a few millimeters thick and containing a Peltier element or its equivalent, and which can, by a small number of conducting wires, be remotely affected, first to passively sense the released latent heat of ice formation, and thereafter to actively, by periodic, short-term heating of the measuring surface cause a melting of an extremely thin layer adjacent to the measuring surface, causing the temperature of this layer to become 0xc2x0 C., followed by momentuous passive sensing indicating whether ice formation has occured or not. Note especially that the device is insensitive to the purity of the ice layer, for example contents of sand, and also for its surface nature as well as for possible vibrations etc.